One-to-one torque coupling

ABSTRACT

A one-to-one torque coupling includes a centre member, left and right side members, and a plurality of torque transfer elements. The centre member is disposed between the side members, has a main axis of rotation and includes a plurality of holes disposed about the main axis at a radius. The side members each have a common secondary axis of rotation that is parallel to and offset from the main axis. Each side member also includes a plurality of holes that are congruent with the holes in the centre member and are disposed about the secondary axis at the radius. The torque transfer elements extend through the holes of the centre member into the holes of the side members, and rotate about a third axis that is parallel to and disposed midway between the main axis and the secondary axis. The torque transfer elements transfer torque between the centre member and the side members through rolling contact between the torque transfer elements and the holes of the centre and side members.

RELATED APPLICATIONS

This patent application claims the benefit of and is a National StageApplication under 35 C.F.R. § 371 of International Application No.PCT/CA2015/050735, filed Aug. 5, 2015, and titled “One-to-One TorqueCoupling,” which claims the benefit of the filing date of U.S. PatentApplication No. 62/033,554, entitled “One-to-One Torque Coupling”, filedAug. 5, 2014, the contents of each of which are hereby incorporatedherein by reference in their entireties.

FIELD

This patent application relates to couplings and methods fortransmitting power between two rotating components, more particularly,for couplings to transmit power between two components rotating onparallel axes at a pre-defined radial distance apart without changingthe speed or direction of rotation.

BACKGROUND

Devices for transferring power from one axis to a second parallel offsetaxis are well known in the art. Typically this transfer occurs with theuse of gears, chains, sprockets and belts where there is some predefinedchange in speed and torque. If it is desired that there be no speeddifference between the two shafts, prior art typically requires largeand complex components to continuously transfer the power. This becomesof particular concern when the distance between the two rotating shaftsis relatively small.

SUMMARY

By way of overview, this disclosure relates to a torque coupling thatallows for the transfer of torque from a first torque member to a secondtorque member without a change in rotational speed between the torquemembers.

In one aspect, the torque coupling includes a centre member, left andright side members, and a plurality of torque transfer elements. Thecentre member is disposed between the side members, has a main axis ofrotation and includes a plurality of holes that are disposed about themain axis at a radius. The side members each have a common secondaryaxis of rotation that is parallel to and offset from the main axis. Eachside member includes a plurality of holes that are congruent with theholes in the centre member and are disposed about the secondary axis atthe radius.

The torque transfer elements extend through the holes of the centremember into the holes of the side members. The torque transfer elementsrotate about a third axis that is parallel to and disposed midwaybetween the main axis and the secondary axis and transfer torque betweenthe centre member and the side members through rolling contact betweenthe torque transfer elements and the holes of the centre and sidemembers. As a result, torque is transferred between the main axis andthe secondary axis without a change in rotational speed or directionbetween the centre member and the side members.

In one implementation, the holes of the centre member are equally spacedabout the main axis, and the holes of the side members are equallyspaced about the secondary axis. The diameter of the torque transferelements may be greater than the distance between the main axis and thesecondary axis.

The torque transfer elements may comprise cylindrical rollers. Eachcylindrical roller may have a diameter that is mutually independent ofthe distance between the main axis and the secondary axis. Alternately,the torque transfer elements may comprise elliptical rollers, orspherical rollers.

In another aspect, the torque coupling includes a centre member, leftand right side members, first and second torque members, and a pluralityof torque transfer elements.

The centre member is disposed between the side members, has a main axisof rotation and includes a plurality of holes that are disposed aboutthe main axis at a radius. The side members each have a common secondaryaxis of rotation that is parallel to and offset from the main axis. Eachside member includes a plurality of holes that are disposed about thesecondary axis at the radius. The first torque member is coupled to thecentre member, and the second torque member is coupled to at least oneof the side members.

The torque transfer elements extend through the holes of the centremember into the holes of the side members. The torque transfer elementsrotate about a third axis that is parallel to and disposed midwaybetween the main axis and the secondary axis and transfer torque betweenthe first torque member and the second torque member through rollingcontact between the torque transfer elements and the holes of the centreand side members. As a result, torque is transferred between the mainaxis and the secondary axis without a change in rotational speed ordirection between the first torque member and the second torque member.

In one implementation, the first torque member has a fixed axis ofrotation that coincides with the main axis, and the second torque memberhas a fixed axis of rotation that coincides with the secondary axis. Inanother implementation, the second torque member has an axis of rotationthat orbits eccentrically about the fixed axis of rotation.

In another aspect, the torque coupling includes a centre member, leftand right side members, and a plurality of crescent elements. The centremember rotates about a primary axis, and includes a plurality of equallyspaced holes that are centered about an assembly centerline. The sidemembers rotate together about a secondary axis, and each include aplurality of equally spaced cut outs that are centered about a secondaryparallel offset centerline. The crescent elements are supported withinthe centre member by full complement roller bearings with attachment tothe left and right side members by pins.

The crescent elements transfer torque from rotation about the primaryaxis to rotation about the secondary axis without changing therotational speed or direction.

The crescent elements contain a primary axis and a secondary axis, eachaxis being separated by the same distance as the primary and secondaryaxis of the centre member and left and right side members respectively.

In one implementation, a coplanar gear set that consists of an inputgear and an output gear is connected in such a manner that one of thegears rotates on the same axis as the left and right side members, whilethe other gear rotates on the same axis as the centre member. In anotherimplementation, the left and right side members are rigidly coupled toone of the input or output gears. In yet another implementation, thecentre member is rigidly coupled to one of the input or output gears.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects are better understood when the followingdetailed description is read with reference to the accompanyingdrawings, in which:

FIG. 1 is an isometric view of a prior art device that allows thetransfer of torque between parallel offset axes in a 1:1 ratio;

FIG. 2 is an isometric view of another prior art device that allows thetransfer of torque between parallel offset axes in a 1:1 ratio;

FIG. 3 shows an isometric view of a first embodiment of a one-to-onetorque coupling with cylindrical roller elements;

FIG. 4 shows an exploded view of the embodiment depicted in FIG. 3 withthe addition different features that help to keep the cylindricalrollers in place;

FIG. 5 shows an end view of the embodiment depicted in FIG. 3;

FIG. 6 illustrates a longitudinal cross-sectional view of a firstembodiment of a bi-ratio state module incorporating a one-to-one torquecoupling;

FIG. 6a illustrates a transverse cross-sectional view of the bi-ratiostate module depicted in FIG. 6;

FIG. 7 illustrates a cross-sectional view of a second embodiment of abi-ratio state module incorporating a one-to-one torque coupling;

FIG. 8 illustrates a cross-sectional view of a third embodiment of abi-ratio state module that is kinematically identical to the secondbi-ratio state module depicted in FIG. 7 with wet friction clutchesreplacing the concentric V-groove torque couplings;

FIG. 9 illustrates a one-to-one coupling that is integral with acoplanar gear set;

FIG. 10 illustrates a sketch showing the eccentric rotation of a secondtorque member about a first torque member;

FIG. 11 illustrates a cross-sectional view of a high-ratio module inwhich the centre member of the one-to-one torque coupling is grounded;

FIG. 12 illustrates a conventional coplanar reverted gear train loop;

FIG. 13 illustrates a cross-sectional view of a second embodiment of theone-to-one torque coupling incorporating elliptical rollers;

FIG. 14 illustrates a cross-sectional view of a third embodiment of theone-to-one torque coupling incorporating spherical rollers; and

FIG. 15 illustrates a cross-sectional view of a fourth embodiment of theone-to-one torque coupling incorporating multi-crescent elements.

DETAILS

Examples will now be described more fully hereinafter with reference tothe accompanying drawings in which example embodiments are shown.Whenever possible, the same reference numerals are used throughout thedrawings to refer to the same or like parts. However, aspects may embodymany different forms and should not be construed as limited to theembodiments set forth herein.

FIG. 1 depicts a prior art mechanism that allows for the transfer oftorque between parallel offset axes in a 1:1 ratio. The mechanismconsists of a driven torque member 1 that rotates about a primary fixedaxis a′ and a driver torque member 2 that rotates about a secondaryfixed axis a″ that is parallel to and offset from the primary fixed axisa′. The spigots 1 a are integral with the driven torque member 1 andprotrude into the circular thru holes 2 a of the driver torque member 2.Assuming a clockwise rotation, torque is transferred from the drivertorque member 2 to the driven torque member 1 through sliding contactbetween the circular thru holes 2 a and the spigots 1 a. A disadvantageof this mechanism is that torque is transferred (theoretically) throughsliding contact from the initial point of contact 3 a to the end pointof contact 3 b.

Oldham's coupling, shown in FIG. 2, is another mechanism fortransferring torque in a 1:1 ratio. Described in “Kinematics” by R. J.Durley, Oldham's coupling includes three elements: a first disc 4coupled to an input torque member 10 that rotates about a primary fixedaxis b′, a second disc 5 coupled to an output torque member 11 thatrotates about a secondary fixed axis b″ that is parallel to and offsetfrom the primary fixed axis b′, and a third centre disc 6 that is joinedto the first and second said discs by tongue 6 a and groove 4 a, 5 aconnections. The grooves (or slots) 4 a, 5 a in end members 4 and 5 areoriented such that they are perpendicular to one another. The tongues(or keys) 6 a on each side the centre member 6 are placed within theirrespective grooves on the end members to form sliding pairs that allowthe transfer of torque from said input torque member to said outputtorque member. This mechanism is particularly susceptible to abrasionbetween the keys and slots due to the sliding contact, which can lead tohigh frictional losses and decreased performance.

Referring now to FIGS. 3, 4 and 5, a one-to-one torque coupling 100 isshown comprising a centre member 101, a left side member 102, a rightside member 103, and a plurality of torque transfer elements 104. Thecentre member 101 rotates about a main axis c1. The left side member 102and the right side member 103 rotate about a secondary axis c2 that isparallel to and offset from the main axis c1. The torque transferelements 104 rotate about a third axis c3 that is parallel to and offsetfrom the main axis c1 and the secondary axis c2 and that is locatedmidway between the main axis c1 and the secondary axis c2.

Preferably, the centre member 101 and side members 102, 103 all have anequal number of congruent circular thru-holes (101 a, 102 a, 103 a).Further, preferably the thru-holes on each member 101, 102, 103 areevenly spaced at a respective radius about the member's rotational axis,and the radius (r1) at which the thru-holes 101 a are disposed (aboutthe main axis c1) on the centre member 101 is equal to the radius (r2)at which the thru-holes 102 a, 103 a are disposed (about the secondaryaxis c2) on the side members 102, 103. The number of the thru-holes 101a, 102 a, 103 a can vary depending on the physical size of theone-to-one torque coupling 100 and it is left up to the designer todetermine the optimal number of holes. A greater number of thru-holeswill distribute the torque more evenly within the members 101, 102, 103.However, the structural integrity of the centre member 101 and sidemembers 102,103 can be compromised by having too many holes 101 a, 102a, 103 a.

Preferably, a first torque member (not shown), which rotates about themain axis c1, is attached to the centre member 101, and a second torquemember (not shown), which rotates about the secondary axis c2, isattached to the left and right side members 102 and 103. In theembodiment shown, the centre member 101 is configured for attachment tothe first torque member through a tabbed connection on its outerdiameter. The left and right side members 102, 103 function together asa single unit and are configured for attachment to the second torquemember through spline connections on the inner diameters of the sidemembers 102, 103 such that the circular thru-holes 102 a on the leftside member 102 line up axially with the circular thru-holes 103 a onthe right side member 103. However, it is not necessary to use thesespecific types of external connections.

In the embodiment shown, the torque transfer elements 104 comprisecylindrical rollers 104. The cylindrical rollers 104 are disposed withinthe thru-holes of the centre member 101 and the side members 102, 103such that the rollers 104 span the axial length from the thru-holes 102a of the left side member 102, through the thru-holes 101 a in thecentre member 101, to the thru-holes 103 a of the right side member 103.Although the cylindrical rollers 104 are shown as all having the samediameter, the rollers 104 may be of different diameters provided thatthe corresponding thru-holes 101 a, 102 a, 103 a in the centre and sidemembers 101, 102, 103 are appropriately sized and the thru-holes 101 aof the centre member 101 are congruent (size, placement) with thethru-holes 102 a, 103 a of the side members 102, 103. The rollers 104may be sized such that their diameters are equal to the diameter of thecircular holes 101 a (or the diameter of the circular holes 102 a, 103a) less the centre distance of rotation of the first torque member andthe second torque member (i.e. less the distance that the secondary axisc2 is offset from the main axis c1). Or in other terms, the diameter ofthe thru-holes 101 a, 102 a, 103 a may be sized by adding the diameterof the cylindrical rollers 104 to the centre distance of rotation of thecentre and side members 101, 102, 103. An appropriate amount ofclearance may then added to the thru-holes 101 a, 102 a, 103 a to ensurethat the cylindrical rollers 104 do not bind up.

FIG. 4 shows two methods of restricting the axial movement of thecylindrical rollers 104 within the thru-holes 101 a, 102 a, 103 a. Thefirst method involves the use of end caps 105, 106 which arerespectively attached to the end surfaces of the left and right sidemembers 102, 103. The second method involves the use of circlips 107which are each fixed to a respective roller 104 (see FIG. 4b ). In thelatter case, preferably the thru-holes 101 a in the centre member 101are recessed (see FIG. 4a ) to allow for the circlip 107 to fit inbetween the centre member 101 and the right side member 103. In certainassemblies, it is also possible for design elements adjacent to the leftand right side members 102, 103 to act as the end caps 105 and 106.

Torque is transferred from the first torque member to the second torquemember (or from the second torque member to the first torque member)without any change in speed or direction through smooth rolling contactbetween the cylindrical rollers 104 and the inner surfaces of thecircular thru-holes in the centre member 101 and the side members 102,103. This type of contact is ideal in terms of minimizing contact stressas the cylindrical rollers 104 and the inner surfaces of the circularthru-holes create a ‘pin-in-trough’ contact interface that maximizes thecontact surface area.

Although, as discussed above, the diameter of the thru-holes may besized by adding the diameter of the cylindrical rollers 104 to thecentre distance of rotation of the centre and side members 101, 102,103, in general the geometry (or diameter) of the thru-holes 101 a, 102a, 103 a in the centre and side members 101, 102, 103 is mutuallyindependent of the centre distance of rotation of the centre member 101and the side members 102, 103 and depends solely on the diameter of thecylindrical rollers 104. This is advantageous since the roller diametercan be made larger than the centre distance of rotation of the centreand side members 101, 102, 103, if desired, and there is potential togain more capacity from the rollers 104 of the one-to-one coupling. FIG.5 shows an end view of the one-to-one torque coupling 100 with the rightend cap 106 removed. This clearly shows that the roller diameter islarger than the centre distance of rotation of the centre and sidemembers 101, 102, 103.

The one-to-one torque coupling 100 works particularly well when used inconjunction with low ratio external/internal reverted coplanar geartrain loops that incorporate addendum tooth form flanks, previouslydescribed by the instant inventor in U.S. Pat. No. 6,126,566, becausethe centre distance between such gear set pairs is typically small.Traditional involute tooth flanks can also be used in place of theaddendum tooth form flanks however, there are limitations in terms ofstrength capacity and packaging. Therefore, the addendum tooth formflanks are preferred.

An assembly advantage is that the one-to-one torque coupling 100 canreplace a secondary gear set that would be required to transfer torquefrom the output gear of the external/internal coplanar gear loop back tothe main axis of the input torque member. Therefore, a single gear setcan be used with the one-to-one torque coupling to provide a very slightincrease or decrease in ratio within a tight package with the input andoutput being coaxial. In combination with concentric V-groove torquecouplings, such as those described by the instant inventor in U.S. Pat.No. 8,764,597, the assembly described above can be stacked one besidethe other providing a compact series of ‘on-off’ ratio state modulesthat can be supported by a single centering shaft. Controlling thebi-ratio state modules using an interactive clutch member in theconcentric V-groove torque couplings is also described by the instantinventor in U.S. Pat. No. 6,669,594.

FIG. 6, illustrates in cross-section, a bi-ratio state module, denotedgenerally as 200, incorporating an external/internal coplanar gear setwith addendum tooth form flanks and a one-to-one torque coupling(comprising centre member 205, side members 204 a, 204 b, andcylindrical rollers 206) in which a pair of concentric V-groove torquecouplings, consisting of inner V-groove coupling (comprising centreclutch member 208 a disposed between interactive member 207 and clutchend member 208 b) and outer V-groove coupling (comprising interactivemember 207 disposed between clutch end members 209 a, 209 b), controlthe output state of the module. The one-to-one torque coupling ensuresthat the output is passed along the main axis c1. This configuration ofthe one-to-one coupling is slightly different from the one-to-onecoupling 100 depicted in FIGS. 3, 4 and 5 since the centre member 205 isburied within the side members 204 a and 204 b and the connection to apotential external torque member does not line up axially with thecentre member 205. Torque can be transferred in either direction throughthe bi-ratio state module, meaning that pinion 201 or centre member 205can act as either the input or output member.

For the purpose of explaining the module's function, pinion 201 is takenas the input member and centre member 205 is taken as the output member.Pinion 201, which rotates about the main axis c1, and annular gear 202,which rotates about a parallel offset axis c2, together with eccentricmember 203, form an external/internal coplanar gear set that acts as theinput to the bi-ratio state module. Intermediate member 211 couplesinteractive member 207 of the inner and outer concentric V-groove torquecouplings to the input pinion 201. Interactive member 207 is axiallymoveable on eccentric member 203, which is supported by a needle rollerbearing n1 that is centred about the offset axis c2.

When the outer concentric V-groove torque coupling is activatedhydraulically or pneumatically, the inner concentric V-groove torquecoupling is forced into an open state and the eccentric member 203 isgrounded to the housing 210, causing a fixed gear ratio to be passed tothe one-to-one torque coupling. When the outer concentric V-groovetorque coupling is deactivated, a wave spring activates the innerconcentric V-groove torque coupling and eccentric member 203 is directlycoupled to the input pinion 201, causing a 1:1 ratio to be passed to theone-to-one torque coupling. The one-to-one torque coupling thentransmits either of the ratio states (fixed or 1:1) from the side plates204 a and 204 b, which rotate about axis c2, to the centre member 205via smooth rolling contact of the cylindrical rollers 206.

FIG. 7, illustrates in cross-section, a second configuration of abi-ratio state module, denoted generally as 300, incorporating anexternal/internal coplanar gear set with addendum tooth form flanks anda one-to-one torque coupling (comprising centre member 303, side members304 a, 304 b, and cylindrical rollers 305) in which a pair of concentricV-groove torque couplings, consisting of inner V-groove coupling(comprising centre clutch member 309 disposed between interactive member310 a and clutch end member 308) and outer V-groove coupling (comprisinginteractive members 310 a and 310 b disposed between end pistons 311 a,311 b), control the output state of the module. Again, the one-to-onetorque coupling ensures that the output is passed along the main axisc1.

Pinion 301 or shaft 307 (which is attached to side members 304 a and 304b) can act as either the input or output member for the bi-ratio statemodule. However, for the purpose of explaining this module's function,pinion 301 is taken as the input member and shaft 307 is taken as theoutput member. Pinion 301, which rotates about the main axis c1, andannular gear 302, which is supported by bearing n1 and rotates about anoffset axis c2, form a coplanar gear set that acts as the input to thebi-ratio state module. Intermediate member 313 couples the input pinion301 to the centre member 309 of the inner concentric V-groove torquecoupling. Interactive member 310 a is axially moveable on the housing308 of the inner concentric V-groove torque coupling and rotates aboutthe main axis c1.

When the end pistons 311 a and 311 b of the outer concentric V-groovetorque coupling are activated hydraulically or pneumatically, end piston311 b acts as a rigid support for bearing n1 causing annular gear 302 torotate about a fixed axis c2. Therefore, a fixed ratio is passed fromthe coplanar gear set to the centre member 303 of the one-to-onecoupling. A floating eccentric bearing support 306 helps to stabilizethe centre member 303 as it rotates about the fixed offset axis c2. Whenthe end pistons 311 a, 311 b are deactivated, a wave spring s1 activatesthe inner concentric V-groove torque coupling causing the input pinion301 to be directly coupled to the housing 308, forcing annular gear 302to rotate eccentrically about the main axis c1 in a 1:1 ratio state withthe input pinion. Therefore, a 1:1 ratio is passed from the annular gear302 to the centre member 303 of the one-to-one torque coupling. Torqueis then transferred from the centre member 303 to the side members 304 aand 304 b via the cylindrical rollers 305 to the output shaft 307, whichrotates about the main axis c1.

FIG. 8, illustrates in cross-section, an identical configuration of theone-to-one torque coupling depicted in FIG. 7, denoted generally as 350,with the exception that wet friction clutches 351 a and 351 b are usedin place of the concentric V-groove torque couplings. The wet frictionclutches have much less capacity than the concentric V-groove couplings,but are of significantly lower cost. Therefore, it is left up to thedesigner to choose which type of coupling to use in each particularapplication of the art. In FIG. 7, the input pinion and output shaft(301 and 307, respectively) rotate concentrically on the same side ofthe embodiment, whereas in FIG. 8, the input pinion and output pinion(352 and 353, respectively) rotate on opposite sides of the embodiedmodule. Each embodiment can be used in combination with either wetfriction clutch discs or concentric V-groove couplings.

FIG. 9 shows a configuration of the one-to-one torque coupling in whichthe centre member 376 is integral with shaft 375 and the right sidemember 377 b is integral with pinion 377 b′ of the coplanar gear set(377 b′ and 379). The left side member 377 a is coupled to the rightside member 377 b via a spline connection. The shaft/centre member(375/376) and annular gear 379 rotate about the main axis c1 and theright and left side members/pinion (377 a, 377 b/377 b′) rotate about aparallel offset axis c2. This arrangement creates a high density powertransfer mechanism where torque can be transferred (in either direction)between the shaft 375 and the annular gear 379 via the one-to-oneconnection.

The one-to-one torque coupling 100 also functions if one of the torquemembers rotates eccentrically about the centre of the other torquemember. FIG. 10 shows a coupling 100 in which the first torque memberTM1 has a fixed main axis of rotation c1, and the second torque memberTM2 has an axis of rotation c2 that orbits eccentrically about the mainaxis of rotation c1.

FIG. 11, illustrates in cross-section, a high-ratio module, denotedgenerally as 400, comprising an external/internal coplanar gear set withaddendum tooth form flanks and a one-to-one torque coupling (405, 406 a,406 b, 407). Either member 401 or eccentric member 404 can be the inputor output elements for the high-ratio module however, for the purpose ofexplaining its functionality, member 401 is considered to be the inputmember and eccentric member 404 is considered to be the output member.The concept of the high-ratio module is based on a conventional clustercoplanar reverted gear train loop, previously described by the instantinventor in U.S. Pat. No. 6,126,566, which typically consists of apinion, a cluster, an annular gear, and a cage (or eccentric member).

In a conventional cluster coplanar reverted gear-train loop, denotedgenerally as 450 in FIG. 12, the relationships describing the angularvelocities of its components are

$\omega_{P} = {\frac{k - 1}{k}\omega_{C}\frac{1}{k}\omega_{A}}$$\omega_{CL} = {\frac{c - d}{c}\omega_{C}\frac{d}{c}\omega_{A}}$$k = {\left( \frac{a}{b} \right)\left( \frac{c}{d} \right)}$where ω_(P), ω_(C), ω_(A), and ω_(CL) represent the angular velocitiesof the pinion 451, the cage (or eccentric) 454, the annular gear 453,and the cluster 452 respectively and a, b, c, and d are the number ofteeth on the pinion, inner cluster, outer cluster, and annular gearrespectively. In the high-ratio module 400, the centre member 405 of theone-to-one coupling acts as the pinion 451 of the coplanar reverted loopand the side members 406 a and 406 b act as the ‘b’ mesh of the cluster452. With the centre member 405 fixed to housing 408, the relationshipbetween the annular gear 402 and the eccentric member 404 becomes

$\omega_{{eccentric}\mspace{11mu}{(404)}} = {\frac{1}{1 - k}\omega_{{annular}\mspace{11mu}{gear}\mspace{11mu}{(402)}}}$$k = {\left( \frac{a}{b} \right)\left( \frac{c}{d} \right)}$

The one-to-one coupling implies that

$\frac{a}{b} = 1.$A mechanical advantage is that a very high ratio can be created betweenthe eccentric member 404 and member 401 by choosing an appropriatenumber of teeth on the annular gear 402 and the pinion 403. For example,if the number of teeth on the annular gear 402 and the pinion 403 arechosen to be 60 and 56, respectively, a 15:1 gear reduction results fromthe input member 401 to the eccentric output member 404. Since thecentre member 405 of the one-to-one coupling is fixed, input from theannular gear 402 causes the pinion 403, along with the side members 406a and 406 b, to ‘walk’ around its gear mesh forcing the eccentric member404 to rotate about the main axis c1 through bearing race n2.

FIGS. 13 and 14, illustrate in cross-section, separate embodiments ofthe one-to-one coupling using elliptical and spherical roller elements,504 and 554 respectively, in place of the preferred cylindrical rollers.The elliptical and spherical roller elements, 504 and 554, do notrequire end caps to hold them in place (in a geometric sense), however,as torque is transferred from the centre member to the side members andvice versa, axial forces develop within holes of the one-to-one couplingthat tend to separate the side members from the one-to-one coupling. Tokeep the side members from separating, they are keyed together and heldin place by a plurality of set screws (FIG. 13) and a circlip (FIG. 14).It is left to the designer to select the form of rolling element that isbest suited for their design.

FIG. 15a , illustrates in cross-section, a one-to-one torque coupling600 that incorporates multi-crescent elements 605 in place of theaforementioned roller elements. FIG. 15b shows the centre member 602with the multi-crescent elements 605 located by full complement bearingsn1 and n2. FIGS. 15c and 15d show the right and left side members 603 aand 603 b, respectively, with appropriately shaped cut-outs to acceptpins 604 which are used to hold said side members in place. In thisparticular arrangement, the centre member 602 rotates about a main axisc1 and the side members 603 a and 603 b rotate about an parallel offsetaxis c2. Torque is transferred through the full complement bearings n1and n2 as the eccentric multi-crescent elements rotate within thecircular holes of the centre member 602.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thescope of the invention as defined by the appended claims.

The invention claimed is:
 1. A coupling comprising: a centre member having a main axis of rotation and including a plurality of holes disposed about the main axis at a radius; left and right side members each having a common offset axis of rotation parallel to and offset from the main axis, each said side member including a plurality of holes congruent with the holes in the centre member and disposed about the offset axis at the radius; and a plurality of torque transfer elements extending through the holes of the centre member into the holes of the side members; wherein the centre member is disposed between the side members, and the torque transfer elements comprise cylindrical rollers and rotate about a third axis parallel to and disposed midway between the main axis and the offset axis and transfer torque between the centre member and the side members through rolling contact between the torque transfer elements and the holes of the centre and side members, and wherein each said cylindrical roller has a diameter that is greater than a distance between the main axis and the offset axis.
 2. The coupling according to claim 1, further including end caps coupled to the side members for retaining the torque transfer elements within the holes.
 3. The coupling according to claim 1, wherein one of the torque transfer elements includes a circlip for retaining said one torque transfer element within the respective holes. 